Display device and electronic equipment

ABSTRACT

A display device includes a pixel array section, the pixel array section having pixels arranged in a matrix form, at least one of the pixels including an electro-optical element, a write transistor, a capacitor, a drive transistor, and a switching transistor. A write scan line is disposed for each pixel row of the pixel array section and adapted to convey a write signal to be applied to a gate electrode of the write transistor. The wiring structure of the write scan line does not cross a wiring pattern connected to a gate electrode of the drive transistor.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.16/108,715, filed Aug. 22, 2018, which is a Continuation Application ofU.S. patent application Ser. No. 15/683,919, filed Aug. 23, 2017, nowU.S. Pat. No. 10,102,804, issued on Oct. 16, 2018, which is aContinuation Application of U.S. patent application Ser. No. 15/334,342,filed Oct. 26, 2016, now U.S. Pat. No. 9,767,731, issued on Sep. 19,2017, which is a Continuation Application of U.S. patent applicationSer. No. 14/826,277, filed on Aug. 14, 2015, now U.S. Pat. No.9,508,780, issued on Nov. 29, 2016, which is a Continuation Applicationof U.S. patent application Ser. No. 14/465,079, filed on Aug. 21, 2014,now U.S. Pat. No. 9,142,571 issued on Sep. 22, 2015, which is aContinuation Application of U.S. patent application Ser. No. 14/246,234,filed on Apr. 7, 2014, now U.S. Pat. No. 9,214,477 issued on Dec. 15,2015, which is a Continuation Application of Ser. No. 13/548,473, filedon Jul. 13, 2012, now U.S. Pat. No. 8,743,026, issued on Jun. 3, 2014,which is a Continuation Application of U.S. patent application Ser. No.12/219,401, filed on Jul. 22, 2008, now U.S. Pat. No. 8,237,631, issuedon Aug. 7, 2012, which in turn claims priority from Japanese ApplicationNo. 2007-211624, filed on Aug. 15, 2007, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a display device and electronicequipment, and more particularly to a flat panel display device andelectronic equipment having the same in which pixels, each incorporatingan electro-optical element, are disposed in a matrix form.

2. Description of Related Art

In the field of image display device, flat panel display devices havingpixels (pixel circuits), each incorporating an electro-optical element,disposed in a matrix form, are rapidly becoming widespread. Among flatpanel display devices, the development and commercialization of organicEL display devices using organic EL (Electro Luminescence) elements havebeen continuing at a steady pace. An organic EL element is a type ofcurrent-driven electro-optical element whose light emission brightnesschanges according to the current flowing through the element. This typeof element relies on the phenomenon that an organic thin film emitslight when applied with an electric field.

An organic EL display device has the following features. That is, it islow in power consumption because organic EL elements can be driven by avoltage of 10V or less. Besides, organic EL elements are self-luminous.Therefore, an organic EL display device offers higher image visibilityas compared to a liquid crystal display device designed to display animage by controlling the light intensity from the light source(backlight) for each of the pixels containing liquid crystal cells.Further, an organic EL display device requires no lighting members suchas backlight as needed for a liquid crystal display device, thus makingit easier to reduce weight and thickness. Still further, organic ELelements are extremely fast in response speed or several μ seconds orso. This provides a moving image free from afterimage.

An organic EL display device can be either simple (passive)-matrix oractive-matrix driven as with a liquid crystal display device. It shouldbe noted, however, that a simple matrix display device has some problemsalthough simple in construction. Such problems include difficulty inimplementing a large high-definition display device because the lightemission period of the electro-optical elements diminishes with increasein the number of scan lines (i.e., number of pixels).

For this reason, the development of active matrix display devices hasbeen going on at a brisk pace in recent years. Such display devicescontrol the current flowing through the electro-optical element with anactive element such as insulating gate field effect transistor(typically, thin film transistor or TFT) provided in the same pixelcircuit as the electro-optical element. In an active matrix displaydevice, the electro-optical elements maintain light emission over aframe interval. As a result, a large high-definition display device canbe implemented with ease.

Incidentally, the I-V characteristic (current-voltage characteristic) ofthe organic EL element is typically known to deteriorate over time(so-called deterioration over time). In a pixel circuit using anN-channel TFT as a transistor adapted to current-drive the organic ELelement (hereinafter written as “drive transistor”), the organic ELelement is connected to the source of the drive transistor. Therefore,if the I-V characteristic of the organic EL element deteriorates overtime, a gate-to-source voltage Vgs of the drive transistor changes, thuschanging the light emission brightness of the same element.

This will be described more specifically below. The source potential ofthe drive transistor is determined by the operating point between thedrive transistor and organic EL element. If the I-V characteristic ofthe organic EL element deteriorates, the operating point between thedrive transistor and organic EL element will change. As a result, thesame voltage applied to the gate of the drive transistor changes thesource potential of the drive transistor. This changes thegate-to-source voltage Vgs of the drive transistor, thus changing thecurrent level flowing through the drive transistor. Therefore, thecurrent level flowing through the organic EL element also changes. As aresult, the light emission brightness of the organic EL element changes.

In a pixel circuit using a polysilicon TFT, on the other hand, athreshold voltage Vth of the drive transistor changes over time, and thethreshold voltage Vth is different from one pixel to another due to themanufacturing process variation (the transistors have differentcharacteristics), in addition to the deterioration of the I-Vcharacteristic over time.

If the threshold voltage Vth of the drive transistor is different fromone pixel to another, the current level flowing through the drivetransistor varies from one pixel to another. Therefore, the same voltageapplied to the gates of the drive transistors leads to a difference inlight emission brightness between the pixels, thus impairing the screenuniformity.

Therefore, the compensation and correction functions are provided ineach of the pixels to ensure immunity to deterioration of the I-Vcharacteristic of the organic EL element over time and variation in thethreshold voltage Vth of the drive transistor over time, thusmaintaining the light emission brightness of the organic EL elementconstant (refer, for example, to Japanese Patent Laid-Open No.2005-345722). The compensation function compensates for the variation incharacteristic of the organic EL element by the transistor betweenpixels.

As described above, each of the pixels has the compensation andcorrection functions so as to compensate bootstrapping action. Thecorrection function corrects the variation in the threshold voltage Vthof the drive for the variation in characteristic of the organic ELelement by the bootstrapping action and correct the variation in thethreshold voltage Vth of the drive transistor. This ensures immunity todeterioration of the I-V characteristic of the organic EL element overtime and variation in the threshold voltage Vth of the drive transistorover time, thus maintaining the light emission brightness of the organicEL element constant.

SUMMARY OF THE INVENTION

In the related art described in Japanese Patent Laid-Open No.2005-345722, a video signal supplied via a signal line on a pixel row bypixel row basis is sampled by a write transistor (sampling transistor)and written to the gate electrode of the drive transistor. Then, theswitching transistor connected to the drain of the drive transistorconducts. This causes a current to flow through the drive transistor,thus achieving the bootstrapping action.

More specifically, as a current flows through the drive transistor, thesource potential of the drive transistor increases. At this time, thegate electrode of the drive transistor is floating because the writetransistor is not conducting. As a result, the gate potential increasesas the source potential increases because of the action of a holdingcapacitance connected between the gate and source electrodes of thedrive transistor. This is the bootstrapping action.

In this bootstrapping action, an increment ΔVs of the source potentialVs of the drive transistor and an increment ΔVg of the gate potential Vgof the same transistor are ideally equal to each other. That is, abootstrap gain Gbst (=ΔVg/ΔVs), namely, the ratio between the incrementΔVs of the source potential Vs and the increment ΔVg of the gatepotential Vg, is unity.

In the presence of parasitic capacitance coupled to the gate electrode,however, the charge is shared between the parasitic and holdingcapacitances. This reduces the bootstrap gain Gbst, making the incrementΔVg of the gate potential Vg smaller than the increment ΔVs of thesource potential Vs (the details thereof will be described later).

That is, the gate-to-source potential difference of the drive transistoris smaller than before the bootstrapping action begins. This makes itimpossible to secure a current required as the drive current to flowthrough the organic EL element, namely, a current appropriate to thevideo signal voltage written by the write transistor. As a result, thelight emission brightness of the pixel determined by the currentdiminishes, thus resulting in deteriorated image quality due to unevenbrightness.

In light of the foregoing, it is desirable to provide a display deviceand electronic equipment having the same which can minimize parasiticcapacitance, a contributor to inhibiting the normal bootstrappingaction, so as to suppress the reduction of light emission brightnesscaused by the parasitic capacitance.

The display device according to one embodiment of the present inventionincludes a pixel array section, write scan line and correction scanline. The pixel array section includes pixels arranged in a matrix form.Each of the pixels includes an electro-optical element, write transistoradapted to write a video signal and holding capacitance adapted to holdthe video signal written by the write transistor. Each of the pixelsfurther includes a drive transistor adapted to drive the electro-opticalelement based on the video signal held by the holding capacitance. Eachof the pixels still further includes a switching transistor adapted toselectively write a reference potential serving as a reference for thevideo signal to the gate electrode of the drive transistor. The writescan line is disposed for each of the pixel rows of the pixel arraysection. The write scan line conveys a write signal to be applied to thegate electrode of the write transistor. The correction scan line isdisposed for each of the pixel rows of the pixel array section. Thecorrection scan line conveys a correction scan signal to be applied tothe gate electrode of the switching transistor. The write scan line isprovided so as not to intersect with the wiring pattern connected to thegate electrode of the drive transistor.

In the display device configured as described above and electronicequipment having the same, the write scan line, and preferably both thewrite scan line and light emission control scan line, do not intersectwith the wiring pattern connected to the gate electrode of the drivetransistor. This prevents parasitic capacitance from being coupled tothe gate electrode of the drive transistor. Or, this minimizes parasiticcapacitance coupled to the gate electrode of the drive transistor. As aresult, the bootstrap gain Gbst during the bootstrapping action can bebrought to unity or close thereto. This makes it possible to secure acurrent appropriate to the video signal voltage written by the writetransistor as the drive current to flow through the organic EL element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram illustrating the schematicconfiguration of an organic EL display device according to anapplication example of the present invention;

FIG. 2 is a circuit diagram illustrating a specific example of theconfiguration of a pixel (pixel circuit);

FIG. 3 is a sectional view illustrating an example of sectionalstructure of the pixel;

FIG. 4 is a timing waveform diagram for describing the basic circuitoperation of the organic EL display device according to the applicationexample of the present invention;

FIG. 5 is a circuit diagram illustrating the arrangement of the pixelcomponents in a typical layout;

FIG. 6 is a plan pattern view schematically illustrating the pixelcomponents in a typical layout;

FIG. 7 is a circuit diagram illustrating the arrangement of the pixelcomponents in a layout according to an embodiment of the presentinvention;

FIG. 8 is a plan pattern view diagrammatically illustrating the pixelcomponents in the layout according to the embodiment of the presentinvention;

FIG. 9 is a perspective view illustrating the appearance of a televisionset to which the present invention is applied;

FIGS. 10A and 10B are perspective views illustrating the appearance of adigital camera to which the present invention is applied, and FIG. 10Ais a perspective view as seen from the front, and FIG. 10B is aperspective view as seen from the rear;

FIG. 11 is a perspective view illustrating the appearance of a laptoppersonal computer to which the present invention is applied;

FIG. 12 is a perspective view illustrating the appearance of a videocamcorder to which the present invention is applied; and

FIGS. 13A to 13G are external views illustrating a mobile phone to whichthe present invention is applied, and FIG. 13A is a front view of themobile phone in an open position, FIG. 13B is a side view thereof, FIG.13C is a front view thereof in a closed position, FIG. 13D is a leftside view thereof, FIG. 13E is a right side view thereof, FIG. 13F is atop view thereof, and FIG. 13G is a bottom view thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention minimizes parasitic capacitance, a contributor toinhibiting the normal bootstrapping action, thus suppressing thereduction of light emission brightness caused by the parasiticcapacitance and providing improved image quality.

The preferred embodiment of the present invention will be describedbelow with reference to the accompanying drawings.

System Configuration

FIG. 1 is a system configuration diagram illustrating the schematicconfiguration of an active matrix display device to which the presentinvention is applied. Here, a description will be given taking, as anexample, an active matrix organic EL display device. The organic ELdisplay device uses, as a light emitting element of each of the pixels(pixel circuits), an organic EL element (organic electroluminescentelement) which is a current-driven electro-optical element whose lightemission brightness changes according to the current flowing through theelement.

As illustrated in FIG. 1, an organic EL display device 10 according tothe present application example includes a pixel array section 30 anddriving sections. The pixel array section 30 has pixels 20 arrangedtwo-dimensionally in a matrix form. The driving sections are disposedaround the pixel array section 30 and adapted to drive the pixels 20.Among the driving sections adapted to drive the pixels 20 are a writescan circuit 40, light emission drive scan circuit 50, first and secondcorrection scan circuits 60 and 70 and horizontal drive circuit 80.

The pixel array section 30 is typically formed on a transparentinsulating substrate such as glass substrate to provide a flat panelstructure. The same section 30 has one of write scan lines 31-1 to 31-m,one of light emission control scan lines 32-1 to 32-m, one of firstcorrection scan lines 33-1 to 33-m and one of second correction scanlines 34-1 to 34-m disposed for each pixel row for the pixels arrangedin m rows by n columns. Further, the same section 30 has one of signallines (data lines) 35-1 to 35-n disposed for each pixel column.

The pixels 20 of the pixel array section 30 may also be formed withamorphous silicon TFTs (Thin Film Transistors) or low-temperaturepolysilicon TFTs. When low-temperature polysilicon TFTs are used, thewrite scan circuit 40, light emission drive scan circuit 50, first andsecond correction scan circuits 60 and 70 and horizontal drive circuit80 can also be implemented on a display panel (substrate) on which thepixel array section 30 is formed.

The write scan circuit 40 includes shift registers or other components.During the writing of a video signal to the pixels 20 of the pixel arraysection 30, the same circuit 40 sequentially supplies write signals WS1to WSm respectively to the write scan lines 31-1 to 31-m so as to scanthe pixels 20 of the pixel array section 30 in succession on arow-by-row basis (progressive scan).

The light emission drive scan circuit 50 includes shift registers orother components. During the driving of the pixels 20 to emit light, thesame circuit 50 sequentially supplies light emission control signals DS1to DSm respectively to the light emission control scan lines 32-1 to32-m.

The first and second correction scan circuits 60 and 70 include shiftregisters or other components. During the correction operation whichwill be described later, the same circuit 60 supplies first correctionscan signals AZ11 to AZ1 m respectively to the first correction scanlines 33-1 to 33-m as appropriate. The same circuit 70 supplies secondcorrection scan signals AZ21 to AZ2 m respectively to the secondcorrection scan lines 34-1 to 34-m as appropriate.

The horizontal drive circuit 80 supplies a video signal voltage Vsigappropriate to the brightness information (hereinafter may be writtensimply as “signal voltage Vsig”) to the signal lines 35-1 to 35-n insynchronism with the scanning by the write scan circuit 40. Thehorizontal drive circuit 80 writes the signal voltage Vsig, for example,on a row-by-row (line-by-line) basis.

Pixel Circuit

FIG. 2 is a circuit diagram illustrating a specific example of theconfiguration of the pixel (pixel circuit) 20.

As illustrated in FIG. 2, the pixel 20 includes, for example, as a lightemitting element, an organic EL element 21 which is a type ofcurrent-driven electro-optical element whose light emission brightnesschanges according to the current flowing through the element. Inaddition to the same element 21, the pixel 20 includes a drivetransistor 22, write transistor (sampling) transistor 23, switchingtransistors 24 to 26, holding capacitance 27 and auxiliary capacitance28 as its components.

In the pixel 20 configured as described above, N-channel TFTs are usedas the drive transistor 22, write transistor 23 and switchingtransistors 25 and 26. A P-channel TFT is used as the switchingtransistor 24. It should be noted, however, that the combination ofconductivity types of the drive transistor 22, write transistor 23 andswitching transistors 24 to 26 given here is merely an example, and thepresent invention is not limited to this combination.

The organic EL element 21 has its cathode electrode connected to asource potential Vcat (ground potential GND in this case). The drivetransistor 22 is an active element adapted to current-drive the organicEL element 21. The drive transistor 22 has its source electrodeconnected to the anode electrode of the organic EL element 21, thusforming a source-follower circuit.

The write transistor 23 has its drain electrode connected to the signalline 35 (one of 35-1 to 35-n), its source electrode connected to thegate electrode of the drive transistor 22, and its gate electrodeconnected to the scan line 31 (one of 31-1 to 31-m).

The switching transistor 24 has its source electrode connected to asecond source potential Vccp (positive source potential in this case),its drain electrode connected to the drain electrode of the drivetransistor 22, and its gate electrode connected to the light emissioncontrol scan line 32 (one of 32-1 to 32-m).

The switching transistor 25 has its drain electrode connected to theother electrode of the write transistor 23 (gate electrode of the drivetransistor 22), its source electrode connected to a third sourcepotential Vofs, and its gate electrode connected to the first correctionscan line 33 (one of 33-1 to 33-m).

The switching transistor 26 has its drain electrode connected to aconnection node N11 between the source electrode of the drive transistor22 and the anode electrode of the organic EL element 21, its sourceelectrode connected to a fourth source potential Vini (negative sourcepotential in this case), and its gate electrode connected to the secondcorrection scan line 34 (one of 34-1 to 34-m).

The holding capacitance 27 has one of its electrodes connected to aconnection node N12 between the gate electrode of the drive transistor22 and the drain electrode of the write transistor 23. The samecapacitance 27 has its other electrode connected to the connection nodeN11 between the source electrode of the drive transistor 22 and theanode electrode of the organic EL element 21.

The auxiliary capacitance 28 has one of its electrodes connected to theconnection node N11 between the source electrode of the drive transistor22 and the anode electrode of the organic EL element 21. The samecapacitance 28 has its other electrode connected to a fixed potentialsuch as the source potential Vccp. The same capacitance 28 is providedfor auxiliary purposes to supplement the lack of capacitance for theorganic EL element 21. Therefore, the same capacitance 28 is notessential as a component of the pixel 20.

In the pixel 20 whose components are connected according to the aboveconnection relationship, each of the components serves the followingfunction.

That is, the write transistor 23 conducts in response to the write scansignal WS given by the write scan circuit 40 via the write scan line 31.As the same transistor 23 conducts, it samples the input signal voltageVsig supplied via the signal line 35 and writes the same voltage Vsig tothe pixel 20. The input signal voltage Vsig written by the writetransistor 23 is applied to the gate electrode of the drive transistor22 and at the same time held by the holding capacitance 27.

When the switching transistor 24 is conducting, the drive transistor 22is supplied with a current from the second source potential Vccp. As aresult, the drive transistor 22 supplies a drive current appropriate tothe voltage level of the input signal voltage Vsig held by the holdingcapacitance 27 to the organic EL element 21, thus driving the sameelement 21 (current driving).

The drive transistor 22 is designed to operate in the saturation region.Therefore, the drive transistor functions as a constant current source.As a result, a constant drain-to-source current Ids, given by thefollowing formula (1), is supplied to the organic EL element 21 from thedrive transistor 22:Ids=(½)·μ(W/L)Cox(Vgs−Vth)²  (1)

Here, Vth is the threshold voltage of the drive transistor 22, μ themobility of the semiconductor thin film making up the channel of thedrive transistor 22 (hereinafter written simply as “mobility of thedrive transistor 22”), W the channel width, L the channel length, Coxthe gate capacitance per unit area, and Vgs the gate-to-source voltageapplied to the gate relative to the source potential.

The switching transistor 24 conducts in response to the light emissiondrive signal DS given by the light emission drive scan circuit 50 viathe light emission control scan line 32. As the same transistor 24conducts, it supplies a current from the second source potential Vccp tothe drive transistor 22. That is, the switching transistor 24 is a lightemission control transistor adapted to control the supply andinterruption of a current to the drive transistor 22, thus controllingthe light emission and non-light emission of the organic EL element 21for duty driving.

The switching transistor 25 conducts in response to the first correctionscan signal AZ1 given by the first correction scan circuit 60 via thefirst correction scan lines 33. As the same transistor 25 conducts, itinitializes the gate potential Vg of the drive transistor 22 to thethird source potential Vofs ahead of the writing of the video signalvoltage Vsig by the write transistor 23. Here, the third sourcepotential Vofs is set to a potential serving as a reference for thevideo signal (reference potential).

The switching transistor 26 conducts in response to the secondcorrection scan signal AZ2 given by the second correction scan circuit70 via the second correction scan lines 34. As the same transistor 26conducts, it initializes the source potential Vs of the drive transistor22 to the fourth source potential Vini ahead of the writing of the videosignal voltage Vsig by the write transistor 23.

As a condition to guarantee the proper operation of the pixel 20, thefourth source potential Vini is set lower than the potential obtained bysubtracting the threshold voltage Vth of the drive transistor 22 fromthe third source potential Vofs. That is, the level relationship,Vini<Vofs−Vth, holds.

Further, the level obtained by adding a threshold voltage Vthel of theorganic EL element 21 to a cathode potential Vcat (ground potential GNDin this case) of the same element 21 is set higher than the levelobtained by subtracting the threshold voltage Vth of the drivetransistor 22 from the third source potential Vofs. That is, the levelrelationship, Vcat+Vthel>Vofs−Vth(>Vini), holds.

The holding capacitance 27 holds not only the video signal voltage Vsigwritten by the write transistor 23 but also the gate-to-source potentialdifference of the drive transistor 22 over the display period.

Pixel Structure

FIG. 3 is a sectional view illustrating an example of sectionalstructure of the pixel 20. As illustrated in FIG. 3, the pixel 20includes an insulating film 202, insulating planarizing film 203 andwindow insulating film 204 formed successively in this order on a glasssubstrate 201. The glass substrate 201 has the pixel circuits formedthereon, each including the drive transistor 22, write transistor 23 andother components. The pixel 20 also includes the organic EL element 21set at a concave portion 204A of the window insulating film 204.

The organic EL element 21 includes an anode electrode 205 made of ametal or other substance formed on the bottom of the concave portion204A of the window insulating film 204. The same element 21 furtherincludes an organic layer 206 (electron transporting layer,light-emitting layer and hole transporting/injection layer) formed onthe anode electrode 205. The same element 21 still further includes acathode electrode 207 formed commonly for all the pixels on the organiclayer 206. The cathode electrode 207 is made up, for example, of atransparent conductive film.

In the organic EL element 21, the organic layer 206 is formed bydepositing a hole transporting layer 2061, light-emitting layer 2062,electron transporting layer 2063 and electron injection layer (notshown) successively in this order on the anode electrode 205. Then, acurrent flows from the drive transistor 22 shown in FIG. 2 to theorganic layer 206 via the anode electrode 205. This causes electrons andholes to recombine in the light-emitting layer 2062 of the organic layer206, thus causing light to be emitted.

As illustrated in FIG. 3, the organic EL element 21 is formed on theglass substrate 201 having the pixel circuits formed thereon. The sameelement 21 is formed on a pixel-by-pixel basis via the insulating film202, insulating planarizing film 203 and window insulating film 204.After the formation thereof, a sealing substrate 209 is bonded with anadhesive 210 via a passivation film 208, and the organic EL element 21sealed with the sealing substrate 209, thus forming a display panel.

Description of the Circuit Operation

A description will be given next of the basic circuit operation of theactive matrix organic EL display device 10 according to the presentapplication example having the pixels 20, configured as described above,arranged two-dimensionally in a matrix form with reference to the timingwaveform diagram in FIG. 4.

FIG. 4 illustrates the timing relationship during the driving of thepixels 20 on a certain row between the write scan signal WS (one of WS1to WSm) given to the pixels 20 by the write scan circuit 40, the lightemission drive signal DS (one of DS1 to DSm) given to the pixels 20 bythe light emission drive scan circuit 50, and the first and secondcorrection scan signals AZ1 (one of AZ11 to AZ1 m) and AZ2 (one of AZ21to AZ2 m) given to the pixels 20 by the first and second correction scancircuits 60 and 70. FIG. 4 also illustrates the changes of the gatepotential Vg and source potential Vs of the drive transistor 22.

Here, the write transistor 23 and switching transistors 25 and 26 areN-channel transistors. Therefore, the write scan signal WS and first andsecond correction scan signals AZ1 and AZ2 are active at high level(source potential Vccp in this example; hereinafter written as “H”level) and inactive at low level (source potential Vcat (GND) in thisexample; hereinafter written as “L” level). Further, the switchingtransistor 24 is a P-channel transistor. Therefore, the light emissiondrive signal DS is active at “L” level and inactive at “H” level.

At time t1, the light emission drive signal DS changes from “L” to “H”level, bringing the switching transistor 24 out of conduction (OFF). Inthis condition at time t2, the second correction scan signal AZ2 changesfrom “L” to “H” level, bringing the switching transistor 26 intoconduction (ON).

As the switching transistor 26 conducts, the fourth source potentialVini is applied to the source electrode of the drive transistor 22 viathe switching transistor 26. That is, the source potential Vs of thedrive transistor 22 is initialized to the source potential Vini ahead ofthe writing of the video signal voltage Vsig.

At this time, the level relationship, Vini<Vcat+Vthel, holds asmentioned earlier. Therefore, the organic EL element 21 isreverse-biased. As a result, no current flows through the organic ELelement 21, causing it not to emit light.

Next, at time t3, the first correction scan signal AZ1 changes from “L”to “H” level, bringing the switching transistor 25 into conduction.Therefore, the third source potential Vofs is applied to the gateelectrode of the drive transistor 22 via the switching transistor 25.That is, the gate potential Vg of the drive transistor 22 is initializedto the source potential Vofs ahead of the writing of the video signalvoltage Vsig.

At this time, the gate-to-source voltage Vgs of the drive transistor 22takes on the value of Vofs-Vini. Here, the level relationship,Vofs−Vini>Vth, is satisfied as mentioned earlier.

Threshold Correction Period

Next, at time t4, the second correction scan signal AZ2 changes from “H”to “L” level, bringing the switching transistor 26 out of conduction.Then, at time t5, the light emission drive signal DS changes from “H” to“L” level, bringing the switching transistor 24 into conduction. As aresult, a current appropriate to the gate-to-source voltage Vgs of thedrive transistor 22 flows through the same transistor 22 from the sourcepotential Vccp via the switching transistor 24.

At this time, the cathode potential Vcat of the organic EL element 21 ishigher than the source potential Vs of the drive transistor 22.Therefore, the organic EL element 21 is reverse-biased. As a result, thecurrent from the drive transistor 22 flows in the following order, i.e.,the node N11, holding capacitance 27, node N12, switching transistor 25,and source potential Vofs. Therefore, a charge appropriate to thecurrent is stored in the holding capacitance 27.

On the other hand, as the holding capacitance 27 is charged, the sourcepotential Vs of the drive transistor 22 will rise gradually from thesource potential Vini over time. Then, when, after elapse of a giventime, the gate-to-source voltage Vgs of the drive transistor 22 becomesequal to the threshold voltage Vth of the same transistor 22, the sametransistor 22 will go into cutoff.

As the drive transistor 22 goes into cutoff, a current stops flowingthrough the same transistor 22. As a result, the gate-to-source voltageVgs of the drive transistor 22, i.e., the threshold voltage Vth, is heldby the holding capacitance 27 as a threshold correction voltage.

Then, at time t6, the light emission drive signal DS changes from “L” to“H” level, bringing the switching transistor 24 out of conduction. Thisperiod from time t5 to time t6 is a period of time during which thethreshold voltage Vth of the drive transistor 22 is detected and held bythe holding capacitance 27.

Here, this given period from t5 to t6 (t 5-t6) will be referred to asthe threshold correction period for the sake of convenience. Then, attime t7, the first correction scan signal AZ1 changes from “H” to “L”level, bringing the switching transistor 25 out of conduction.

Signal Write Period

Next, at time t8, the write scan signal WS changes from “L” to “H”level, bringing the write transistor 23 into conduction and causing thesame transistor 23 to sample the video signal voltage Vsig and writethis signal to the pixel. As a result, the gate potential Vg of thedrive transistor 22 becomes equal to the signal voltage Vsig.

The same voltage Vsig is held by the holding capacitance 27. At thistime, the source potential Vs of the drive transistor 22 rises relativeto the amplitude of the gate potential Vg of the drive transistor 22 atthe time of sampling by the write transistor 23 due to the capacitivecoupling between the holding capacitance 27 and organic EL element 21.

Here, letting the capacitance value of the organic EL element 21 bedenoted by Coled, the capacitance value of the holding capacitance 27 byCs, the capacitance value of the auxiliary capacitance 28 by Csub andthe increment of the gate potential Vg of the drive transistor by_(Δ)Vg, the increment _(Δ)Vs of the source potential Vs of the drivetransistor is given by the following formula (2):ΔVs=ΔVg×{Cs/(Coled+Cs+Csub)}  (2)

On the other hand, the input signal voltage Vsig written by the writetransistor 23 through sampling is held by the holding capacitance 27 sothat the same voltage Vsig is added to the threshold voltage Vth held bythe same capacitance 27.

At this time, assuming that the write gain of the video signal (ratiobetween the video signal voltage Vsig and voltage held by the holdingcapacitance 27) is unity (ideal value), the voltage held by the holdingcapacitance 27 is Vsig−Vofs+Vth. Here, assuming that Vofs=0V for easierunderstanding, the gate-to-source voltage Vgs is Vsig+Vth.

As described above, the variation of the threshold voltage Vth of thedrive transistor 22 between pixels and the change of the same voltageVth over time can be corrected by holding the threshold voltage Vth inthe holding capacitance 27 in advance. That is, when the drivetransistor 22 is driven by the signal voltage Vsig, the thresholdvoltage Vth of the drive transistor 22 and the threshold voltage Vthheld by the holding capacitance 27 cancel each other. In other words,the threshold voltage Vth is corrected.

This correction operation of the threshold voltage Vth permitscancellation of the impact of the threshold voltage Vth on the drivingof the organic EL element 21 by the drive transistor 22 even in thepresence of a variation of the same voltage Vth between pixels or achange of the same voltage Vth over time. As a result, the lightemission brightness of the organic EL element 21 can be maintainedconstant without being affected by the variation of the thresholdvoltage Vth or the change thereof over time.

Mobility Correction Period

Then, at time t9, the light emission drive signal DS changes from “H” to“L” level with the write transistor 23 remaining in conduction, thusbringing the switching transistor 24 into conduction. As a result, thesupply of a current from the source potential Vccp to the drivetransistor 22 begins. Here, the organic EL element 21 is put intoreverse bias by setting Vofs−Vth<Vthel.

When reverse-biased, the organic EL element 21 exhibits a simplecapacitive characteristic rather than diode characteristic. Therefore,the drain-to-source current Ids flowing through the drive transistor 22is written to a combined capacitance C which is the sum of thecapacitance value Cs of the holding capacitance 27, the capacitancevalue Csub of the auxiliary capacitance 28 and the capacitance valueColed of the capacitive component of the organic EL element 21(=Cs+Csub+Coled). This writing causes the source potential Vs of thedrive transistor 22 to rise.

The increment ΔVs of the source potential Vs of the drive transistor 22acts so that it is subtracted from the gate-to-source voltage Vgs of thedrive transistor 22 held by the holding capacitance 27, in other words,so that the charge stored in the holding capacitance 27 is discharged.This means that a negative feedback is applied. That is, the incrementΔVs of the source potential Vs of the drive transistor 22 is a feedbackamount of the negative feedback. At this time, the gate-to-sourcevoltage Vgs of the drive transistor 22 is Vsig−ΔVs+Vth.

As described above, if the current flowing through the drive transistor22 (drain-to-source current Ids) is negatively fed back to the gateinput (gate-to-source potential difference) of the same transistor 22,the dependence of the drain-to-source current Ids of the same transistor22 on the mobility μ in each of the pixels 20 can be cancelled. That is,the variation of the mobility μ of the same transistor 22 between thepixels can be corrected.

In FIG. 4, a period T (period t9-t10) during which the write scan signalWS is active (“H” level period) and the light emission drive signal DSis active (“L” level period) at the same time, namely, the period duringwhich the write transistor 23 and switching transistor 24 are bothconducting, is referred to as a mobility correction period.

Here, a drive transistor with the relatively high mobility μ and anotherwith the relatively low mobility μ are considered. The source potentialVs of the drive transistor with the high mobility μ rises sharply ascompared to that of the drive transistor with the low mobility μ.Further, the higher the source potential Vs rises, the smaller thegate-to-source voltage Vgs of the drive transistor 22 becomes. As aresult, a current is less likely to flow.

That is, it is possible to cause the same drain-to-source current Ids toflow through the drive transistors 22 with the different mobilities μ byadjusting the mobility correction period T. If the gate-to-sourcevoltage Vgs of the drive transistor 22 determined by the mobilitycorrection period T is retained by the holding capacitance 27, and ifthe current (drain-to-source current Ids) appropriate to thegate-to-source voltage Vgs flows from the drive transistor 22 to theorganic EL element 21, the same element 21 emits light.

Light Emission Period

At time t10, the write scan signal WS falls to “L” level, bringing thewrite transistor 23 out of conduction. As a result, the mobilitycorrection period T ends, and a light emission period begins. In thelight emission period, the source potential Vs of the drive transistor22 rises to the driving voltage of the organic EL element 21.

On the other hand, as the write transistor 23 stops conducting, the gateof the drive transistor 22 is disconnected from the signal line 35 (oneof 35-1 to 35-n) and left floating. Therefore, the gate potential Vgwill rise together with the source potential Vs through thebootstrapping action of the holding capacitance 27.

Then, as the source potential Vs of the drive transistor 22 rises, thereverse bias is removed from the organic EL element 21, bringing thesame element 21 into forward bias. Therefore, the constantdrain-to-source current Ids given by the aforementioned formula (1)flows from the drive transistor 22 to the organic EL element 21, causingthe same element 21 to actually start emitting light.

The relationship between the drain-to-source current Ids andgate-to-source voltage Vgs at this time is given by the followingformula (3) by substituting Vsig−_(Δ)Vs+Vth into Vgs in the formula (1).

$\begin{matrix}{\begin{matrix}{{Ids} = {k\;{µ\left( {{Vgs} - {Vth}} \right)}^{2}}} \\{= {k\;{µ\left( {{Vsig} - {\Delta\;{Vs}}} \right)}^{2}}}\end{matrix}{{{where}\mspace{14mu} k} = {\left( {1/2} \right)\mspace{14mu}\left( {W/L} \right)\mspace{14mu}{{Cox}.}}}} & (3)\end{matrix}$

As is clear from the formula (3), the term of the threshold voltage Vthof the drive transistor 22 is cancelled. The drain-to-source current Idssupplied from the drive transistor 22 to the organic EL element 21 isindependent of the threshold voltage Vth of the drive transistor 22.

Basically, the drain-to-source current Ids of the drive transistor 22 isdetermined by the video signal voltage Vsig. In other words, the organicEL element 21 emits light at the brightness appropriate to the videosignal voltage Vsig without being affected by the variation of thethreshold voltage Vth of the drive transistor 22 between the pixels orthe change thereof over time.

As described above, the threshold voltage Vth of the drive transistor 22is held in advance by the holding capacitance 27 before the writing ofthe video signal voltage Vsig. As a result, the threshold voltage Vth ofthe drive transistor 22 can be cancelled (corrected) so that theconstant drain-to-source current Ids flows through the organic ELelement 21 without being affected by the variation of the same voltageVth between the pixels or the change thereof over time. This provides ahigh quality display image (compensation function for the variation ofVth of the drive transistor 22).

Further, as is clear from the formula (3), the video signal voltage Vsigis corrected with the feedback amount ΔVs by negatively feeding back thedrain-to-source current Ids to the gate input of the drive transistor22. The feedback amount ΔVs acts to cancel the effect of the mobility μin the coefficient part of the formula (3).

Therefore, the drain-to-source current Ids is substantially dependentonly upon the video signal voltage Vsig. That is, the organic EL element21 emits light at the brightness appropriate to the signal voltage Vsigwithout being affected either by the variation of the threshold voltageVth of the drive transistor 22 between the pixels and the change thereofover time or by the variation of the mobility μ of the same transistor22 between the pixels and the change thereof over time. This providesuniform image quality free from banding or uneven brightness.

In the mobility correction period T (t9-t10), the drain-to-sourcecurrent Ids is negatively fed back to the gate input of the drivetransistor 22 so that the signal voltage Vsig is corrected with thefeedback amount ΔVs. As a result, the dependence of the drain-to-sourcecurrent Ids of the drive transistor 22 on the mobility μ is cancelled,thus allowing the drain-to-source current Ids, which is dependent onlyupon the signal voltage Vsig, to flow through the organic EL element 21.This ensures uniform display image quality free from banding or unevenbrightness caused by the variation of the mobility μ of the drivetransistor 22 between the pixels or the change thereof over time(compensation function for the mobility μ of the drive transistor 22).

Here, in the organic EL display device 10 having the pixels 20, eachcontaining a current-driven electro-optical element, i.e., the organicEL element 21, arranged in a matrix form, if the light emission time ofthe organic EL element 21 is long, the I-V characteristic of the sameelement 21 will change. For this reason, the connection node N11 betweenthe anode electrode of the organic EL element 21 and the sourceelectrode of the drive transistor 22 will also change in potential(source potential Vs of the drive transistor 22).

In contrast, in the active matrix organic EL display device 10configured as described above, the gate-to-source voltage Vgs of thedrive transistor 22 is maintained constant thanks to the bootstrappingaction of the holding capacitance 27 connected between the gate andsource electrodes of the drive transistor 22. For this reason, thecurrent flowing through the organic EL element 21 remains unchanged.Therefore, the constant drain-to-source current Ids will continue toflow through the organic EL element 21 even if the I-V characteristic ofthe same element 21 deteriorates. This suppresses the variation of thelight emission brightness of the organic EL element 21 (compensationfunction for a characteristic change of the organic EL element 21).

Pixel Layout

Here, the layout of the components making up the pixel 20, namely, thefive transistors 22 to 26, holding and auxiliary capacitances 27 and 28,write scan line 31, light emission control scan line 32 and first andsecond correction scan lines 33 and 34, will be considered.

Typical Pixel Layout

FIG. 5 is a circuit diagram illustrating the arrangement of the pixelcomponents in a typical layout of the pixel 20. FIG. 6 schematicallyillustrates a plan pattern thereof.

Considering the highly efficient layout of the pixel 20, it would becommon, as illustrated in FIGS. 5 and 6, to dispose the first and secondcorrection scan lines 33 and 34 respectively above and below the pixel20, dispose the write scan line 31 and light emission control scan line32 between the scan lines 33 and 34 and arrange the pixel componentsabove and below the scan lines 31 and 32.

More specifically, the write transistor 23 and switching transistor 25are disposed in the region between the first correction scan line 33 andwrite scan line 31. The drive transistor 22, switching transistor 26 andholding and auxiliary capacitances 27 and 28 are disposed in the regionbetween the light emission control scan line 32 and second correctionscan line 34.

This typical layout is based on the idea to minimize the number ofcontact portions adapted to electrically connect the wiring layers so asto ensure efficiency in the component arrangement. It should be notedthat the signal line 35 adapted to convey the video signal voltage Vsigand source lines 36, 37 and 38 adapted respectively to convey the sourcepotentials Vccp, Vofs and Vini, are disposed along the pixel column (inthe column direction of pixels).

In the plan pattern view shown in FIG. 6, the write scan line 31, lightemission control scan line 32, first and second correction scan lines 33and 34, and the gate electrodes of the transistors 22 to 26 are disposedon the glass substrate 201 (refer to FIG. 3) as the first layer usingmolybdenum (Mo) or other material. The semiconductor layers of thetransistors 22 to 26 are formed as the second layer using polysilicon(PS) or other material. The signal line 35 and source lines 36, 37 and38 are disposed as the third layer using aluminum (Al) or othermaterial.

The positional relationship between these wiring layers is obvious fromthe pixel structure shown in FIG. 3. An insulating film mediates betweenthe first and second layers, and another between the second and thirdlayers. As is clear from FIG. 6, adopting the typical layout describedabove makes it possible to keep the number of contact portions adaptedto electrically connect the wiring layers to about 12.

It should be noted, however, that in the above typical layout, a wiringpattern 306 adapted to electrically connect the gate electrode of thedrive transistor 22, source electrode of the write transistor 23 anddrain electrode of the switching transistor 25 intersects with thewiring patterns of the write scan line 31 and light emission controlscan line 32 (area enclosed by a dashed line in FIGS. 5 and 6).

Problems Attributable to Parasitic Capacitance

As described above, because the wiring pattern 306 to the gate electrodeof the drive transistor 22 intersects with the wiring patterns of thewrite scan line 31 and light emission control scan line 32, a parasiticcapacitance is formed in the intersecting area via the insulating film(which corresponds to the insulating film 202 in FIG. 3). This parasiticcapacitance serves as a parasitic capacitance (Cp) coupled to the gateelectrode of the drive transistor 22 (refer to FIG. 2).

Ideally, the increment ΔVs of the source potential Vs of the drivetransistor should be equal to the increment ΔVg of the gate potential Vgof the same transistor in the bootstrapping action described above. Thatis, the bootstrap gain Gbst should be unity. However, a parasiticcapacitance coupled to the gate electrode of the drive transistor 22leads to distribution of charge between the parasitic capacitance andholding capacitance 27, thus reducing the bootstrap gain Gbst.

Here, letting the capacitance value of the parasitic capacitance coupledto the gate electrode of the drive transistor 22 be denoted by Cp, thebootstrap gain Gbst can be expressed by the following formula:Gbst=ΔVg/ΔVs=Cs/(Cs+Cp)  (4)As is clear from the formula (4), the larger the capacitance value Cp ofthe parasitic capacitance coupled to the gate electrode of the drivetransistor 22, the more the bootstrap gain Gbst drops.

If the bootstrap gain Gbst drops, the increment ΔVg of the gatepotential Vg becomes smaller than the increment ΔVs of the sourcepotential Vs. As a result, the gate-to-source potential difference ofthe drive transistor 22 is smaller than when the bootstrapping actionbegins. This makes it impossible to secure a current appropriate to thevideo signal voltage Vsig written by the write transistor 23 as thedrive current to flow through the organic EL element 21. As a result,the light emission brightness of the organic EL element 21 diminishes,thus resulting in deteriorated image quality due to uneven brightness.

Features of the Present Embodiment

For this reason, the present embodiment ensures freedom from parasiticcapacitance coupled to the gate electrode of the drive transistor 22 bydevising a new layout for the components making up the pixel 20, i.e.,the five transistors 22 to 26 and holding and auxiliary capacitances 27and 28, for the wirings, i.e., the write scan line 31, light emissioncontrol scan line 32 and first and second correction scan lines 33 and34, and particularly for the write scan line 31 and light emissioncontrol scan line 32.

Pixel Layout According to the Present Embodiment

FIG. 7 is a circuit diagram illustrating the component arrangement ofthe pixel 20 in a layout according to the embodiment of the presentinvention. FIG. 8 diagramatically illustrates a plan pattern thereof. InFIGS. 7 and 8, like components are designated by the same referencenumerals as in FIGS. 5 and 6.

As illustrated in FIGS. 7 and 8, in the layout of the pixel 20 accordingto the present embodiment, the first and second correction scan lines 33and 34 are disposed respectively above and below the pixel 20 along thepixel row (in the row direction of pixels). The write scan line 31 andlight emission control scan line 32 are disposed further outward of thescan lines 33 and 34 along the pixel row. The components making up thepixel 20, i.e., the five transistors 22 to 26 and holding and auxiliarycapacitances 27 and 28, are disposed between the first and secondcorrection scan lines 33 and 34.

The source line 36 of the source potential Vccp is disposed on the leftand outward of the components of the pixel 20 along the pixel column.Further, the signal line 35 adapted to convey the video signal voltageVsig and source lines 37 and 38 adapted respectively to convey thesource potentials Vofs and Vini, are disposed on the right and outwardof the components of the pixel 20 along the pixel column.

In the plan pattern view of FIG. 8, the write scan line 31, lightemission control scan line 32, first and second correction scan lines 33and 34, and the gate electrodes of the transistors 22 to 26 are disposedon the glass substrate 201 (refer to FIG. 3) as the first layer usingmolybdenum (Mo) or other material. The semiconductor layers of thetransistors 22 to 26 are formed as the second layer using polysilicon(PS) or other material. The signal line 35 and source lines 36, 37 and38 are disposed as the third layer using aluminum (Al) or othermaterial.

Here, the write scan line 31 is disposed outward of the first correctionscan line 33, that is, on the opposite side of the write transistor 23with the first correction scan line 33 between the write scan line 31and write transistor 23. Therefore, the wiring structure described belowis used between the gate electrode of the write transistor 23 and thewrite scan line 31.

That is, contact between the gate electrode of the write transistor 23(Mo wiring on the first layer) and a wiring pattern (Al wiring) 302 onthe third layer disposed along the pixel column is established by acontact portion 301. Contact between the wiring pattern 302 and writescan line 31 is established by a contact portion 303. This ensureselectrical connection with the write scan line 31.

Further, the light emission control scan line 32 is disposed outward ofthe second correction scan line 34, that is, on the opposite side of theswitching transistor 24 with the second correction scan line 34 betweenthe light emission control scan line 32 and switching transistor 24.Therefore, the wiring structure described below is used between the gateelectrode of the switching transistor 24 and the light emission controlscan line 32.

That is, contact between the gate electrode of the switching transistor24 (Mo wiring on the first layer) and a wiring pattern (Al wiring) 305on the third layer disposed along the pixel column is established by acontact portion 304. Contact between the wiring pattern 305 and lightemission control scan line 32 on the first layer is established by acontact portion 306. This ensures electrical connection with the lightemission control scan line 32.

Advantageous Effects of the Present Embodiment

In the present embodiment, as is clear from the aforementioneddescription and FIGS. 7 and 8, the active matrix organic EL displaydevice 10 having at least the drive transistor 22, write transistor 23connected to the gate electrode of the drive transistor 22, andswitching transistor 25 in each of the pixels has an advantageous wiringstructure. That is, the write scan line 31, and preferably the writescan line 31 and light emission control scan line 32, do not intersectwith the wiring pattern connected to the gate electrode of the drivetransistor 22, i.e., the wiring pattern 306 adapted to electricallyconnect the gate electrode of the drive transistor 22, source electrodeof the write transistor 23 and drain electrode of the switchingtransistor 25.

More specifically, the first correction scan line 33 is disposed outwardof the region where the components of the pixel 20 are disposed. Thewrite scan line 31 is disposed further outward of the first correctionscan line 33. The write scan line 31 is electrically connected to thegate electrode of the write transistor 23 via the wiring pattern 302formed on the wiring layer (third layer in this example) different fromthe wiring layer of the scan lines 31 and 33 (first layer in thisexample). This prevents the write scan line 31 from intersecting withthe wiring pattern 306 connected to the gate electrode of the drivetransistor 22.

Further, the light emission control scan line 32 is disposed on theopposite side of the write scan line 31 with the region where thecomponents of the pixel 20 are disposed between the light emissioncontrol scan line 32 and write scan line 31. The light emission controlscan line 32 is electrically connected to the gate electrode of theswitching transistor 24 (light emission control transistor) via thewiring pattern 305 formed on the wiring layer (third layer in thisexample) different from the wiring layer of the light emission controlscan line 32 (first layer in this example). This prevents the lightemission control scan line 32 from intersecting with the wiring pattern306 connected to the gate electrode of the drive transistor 22.

As described above, the write scan line 31, and preferably both thewrite scan line 31 and light emission control scan line 32, do notintersect with the wiring pattern 306 connected to the gate electrode ofthe drive transistor 22. More specifically, the write scan line 31 isdisposed on one side of the region where the components of the pixel 20are disposed, and the light emission control scan line 32 on the otherside thereof. This ensures freedom from parasitic capacitance coupled tothe gate electrode of the drive transistor 22.

Here, both the write scan line 31 and light emission control scan line32 do not intersect with the wiring pattern 306 connected to the gateelectrode of the drive transistor 22. However, even if at least thewrite scan line 31 does not intersect with the wiring pattern 306, theparasitic capacitance coupled to the gate electrode of the drivetransistor 22 can be reduced as compared to when the write scan line 31and light emission control scan line 32 intersect with the wiringpattern 306 as mentioned earlier.

As described above, the bootstrap gain Gbst during the bootstrappingaction can be brought to unity or close thereto by ensuring freedom fromor minimizing parasitic capacitance coupled to the gate electrode of thedrive transistor 22. This makes it possible to secure a currentappropriate to the video signal voltage Vsig written by the writetransistor 23 as the drive current to flow through the organic ELelement 21. This provides suppressing the reduction of light emissionbrightness caused by the parasitic capacitance. As a result, thereduction of light emission brightness of the organic EL element 21 canbe suppressed, thus providing improved image quality.

The present embodiment requires four more contact portions as comparedto the case in which the aforementioned typical layout is used. Theseadditional contact portions are the two contact portions 301 and 303adapted to electrically connect the write scan line 31 and gateelectrode of the write transistor 23 and the other two contact portions304 and 306 adapted to electrically connect the light emission controlscan line 32 and gate electrode of the switching transistor 24. However,it can be said that the disadvantage of a few more contact portionsrequired is outweighed by improved image quality provided by minimizingparasitic capacitance, a contributor to inhibiting the normalbootstrapping action.

MODIFICATION EXAMPLE

In the above embodiment, a description was given taking, as an example,the organic EL display device each of whose pixels contains fivetransistors, i.e., drive transistor 22, write transistor 23 andswitching transistors 24 to 26. However, the present invention is notlimited to this application example, but applicable to organic ELdisplay devices in general having at least the drive transistor 22,write transistor 23 connected to the gate electrode of the drivetransistor 22 and switching transistor 25.

Further, in the above embodiment, a description was given taking, as anexample, the case in which the present invention was applied to anorganic EL display device using organic EL elements. However, thepresent invention is not limited to this application example, butapplicable to flat panel display devices in general having pixels, eachcontaining an electro-optical element, arranged in a matrix form.

APPLICATION EXAMPLES

The display device according to the present invention described above isapplicable as a display device of electronic equipment across all fieldsincluding those shown in FIGS. 9 to 13, namely, a digital camera, laptoppersonal computer, mobile terminal device such as mobile phone and videocamcorder. These pieces of equipment are designed to display an image orvideo of a video signal fed to or generated inside the electronicequipment.

As described above, if used as a display device of electronic equipmentacross all fields, the display device according to the present inventionminimizes parasitic capacitance, a contributor to inhibiting the normalbootstrapping action, thus suppressing the reduction of light emissionbrightness caused by the parasitic capacitance. This provides improvedimage quality on the display screen in any type of electronic equipment.

It should be noted that the display device according to the presentinvention includes that in a modular form having a sealed configuration.Such a display device corresponds to a display module formed byattaching an opposed section made, for example, of transparent glass tothe pixel array section 30. The aforementioned light-shielding film maybe provided on the transparent opposed section, in addition to filmssuch as color filter and protective film. It should also be noted that acircuit section, FPC (flexible printed circuit) or other circuitry,adapted to allow exchange of signals or other information betweenexternal equipment and the pixel array section, may be provided on thedisplay module.

Specific examples of electronic equipment to which the present inventionis applied will be described below.

FIG. 9 is a perspective view illustrating a television set to which thepresent invention is applied. The television set according to thepresent application example includes a video display screen section 101made up, for example, of a front panel 102, filter glass 103 and otherparts. The television set is manufactured by using the display deviceaccording to the present invention as the video display screen section101.

FIGS. 10A and 10B are perspective views illustrating a digital camera towhich the present invention is applied. FIG. 10A is a perspective viewof the digital camera as seen from the front, and FIG. 10B is aperspective view thereof as seen from the rear. The digital cameraaccording to the present application example includes a flash-emittingsection 111, display section 112, menu switch 113, shutter button 114and other parts. The digital camera is manufactured by using the displaydevice according to the present invention as the display section 112.

FIG. 11 is a perspective view illustrating a laptop personal computer towhich the present invention is applied. The laptop personal computeraccording to the present application example includes, in a main body121, a keyboard 122 adapted to be manipulated for entry of text or otherinformation, a display section 123 adapted to display an image, andother parts. The laptop personal computer is manufactured by using thedisplay device according to the present invention as the display section123.

FIG. 12 is a perspective view illustrating a video camcorder to whichthe present invention is applied. The video camcorder according to thepresent application example includes a main body section 131, lens 132provided on the front-facing side surface to image the subject, imagingstart/stop switch 133, display section 134 and other parts. The videocamcorder is manufactured by using the display device according to thepresent invention as the display section 134.

FIGS. 13A to 13G are perspective views illustrating a mobile terminaldevice such as mobile phone to which the present invention is applied.FIG. 13A is a front view of the mobile phone in an open position. FIG.13B is a side view thereof. FIG. 13C is a front view of the mobile phonein a closed position. FIG. 13D is a left side view. FIG. 13E is a rightside view. FIG. 13F is a top view. FIG. 13G is a bottom view. The mobilephone according to the present application example includes an upperenclosure 141, lower enclosure 142, connecting section (hinge section inthis example) 143, display 144, subdisplay 145, picture light 146,camera 147 and other parts. The mobile phone is manufactured by usingthe display device according to the present invention as the display 144and subdisplay 145.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A display device comprising: a gate of a drivetransistor wired directly to a source of a write transistor and a drainof a first switching transistor; and an electrode of an auxiliarycapacitance wired directly an electrode of a holding capacitance and asource of the drive transistor.
 2. The display device according to claim1, further comprising: another electrode of the holding capacitancewired directly to the source of the write transistor and the gate of thedrive transistor.
 3. The display device according to claim 1, furthercomprising: an anode of an electro-optical element wired directly to theelectrode of the holding capacitance and the electrode of the auxiliarycapacitance.
 4. The display device according to claim 3, furthercomprising: a source of a second switching transistor wired directly toanother electrode of the auxiliary capacitance.
 5. The display deviceaccording to claim 4, further comprising: a source potential line wireddirectly to the source of the second switching transistor.
 6. Thedisplay device according to claim 4, further comprising: a drain of thedrive transistor wired directly to a drain of the second switchingtransistor.
 7. The display device according to claim 4, furthercomprising: a drain of a third switching transistor wired directly tothe electrode of the auxiliary capacitance and the electrode of theholding capacitance.
 8. The display device according to claim 7, furthercomprising: another electrode of the holding capacitance wired directlyto the source of the write transistor and the drain of the firstswitching transistor.